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  • On complete combustion a litre of petrol gives off heat equivalent to 3 × 10^7 J. In a test drive a car weighing 1200 kg, including the mass of driver, runs 15 km per litre while moving with a uniform speed on a surface and air to be uniform

On complete combustion a litre of petrol gives off heat equivalent to 3\times 10^{7} J. In a test drive a car weighing 1200 kg, including the mass of driver, runs 15 km per litre while moving with a uniform speed on a surface and air to be uniform, calculate the force of friction acting on the car during the test drive, if the efficiency of the car engine were 0.5.

Answers (1)

Car engine’s efficiency = 0.5

So, energy given to car through petrol of 1 litre = 0.5 \times 3 \times 10^{7}

Now, the work done by car is F \times S = F \times 15000 J

As we know that the work done by car is against the force of friction, hence equating both can give us the value of friction.

F \times 15000 = 0.5 \times 3\times 10^{7}

F = 1000 N

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